The disclosure of the following priority application is herein incorporated by reference: Japanese Patent Application No. 2000-184407 filed Jun., 20, 2000.
1. Field of the Invention
The present invention relates to a testing apparatus and a testing method that enable non-destructive and non-contact measurement of impurity concentration in a semiconductor material such as a semiconductor wafer, an ingot or an epitaxial grown film and, more specifically, the distribution of the oxygen concentration, the nitrogen concentration and the carbon concentration in the semiconductor material and imaging of the distribution of the impurity concentration thus measured.
2. Description of Related Art
In the semiconductor device industry, impurity concentration such as the oxygen concentration, the nitrogen concentration and the carbon concentration with respect to the impurities contained in the semiconductor material used to manufacture a device are crucial factors that determine the performance of the semiconductor device. Conventionally, the measurement of these impurity concentration is implemented through the Fourier transform infrared spectrophotometry. In Fourier transform infrared spectrophotometry impurity concentration are measured based upon the spectral information obtained by irradiating infrared light on a test-piece.
In the Fourier transform infrared spectrophotometric method adopted in the prior art, measurement can be performed only at one point of a semiconductor material through a single measuring operation, and thus, it takes a great deal of time to complete the measurement of the entire semiconductor material. In addition, it is extremely difficult to achieve imaging of the concentration for viewing the impurity quantity distribution at once. Furthermore, it is virtually impossible to capture a spatial image of the impurities in the entire semiconductor material with a resolution in the order of the light wavelength in the practical application.
An object of the present invention is to provide an impurity concentration testing apparatus and an impurity concentration testing method that enable reproduction of the impurity distribution by measuring and checking the impurity concentration in the entire semiconductor material in a simple manner.
The semiconductor impurity concentration testing apparatus according to the present invention comprises a terahertz pulse light source that irradiates terahertz pulse light onto a semiconductor material, a light detector that detects transmitted pulse light having been transmitted through the semiconductor material, a measurement device that obtains a spectral transmittance based upon a time-series waveform of the electric field intensity of the transmitted pulse light detected by the light detector and an arithmetic operation unit that calculates an impurity concentration in the semiconductor material based upon the spectral transmittance.
The arithmetic operation unit may execute an analysis to calculate the oxygen concentration, the nitrogen concentration and the carbon concentration in the semiconductor material based upon Lambert""s light absorption theory.
The semiconductor impurity concentration testing apparatus according to the present invention may further comprise an image processing device that renders the impurity concentration parameters into a two-dimensional image as a spatial distribution.
In addition, the semiconductor impurity concentration testing apparatus according to the present invention may perform two-dimensional scanning of the surface of the semiconductor material with a condensed terahertz pulse light flux or it may two-dimensionally detect transmitted pulse light having been transmitted through the semiconductor material with the light detector by irradiating an expanded light flux of the terahertz pulse light in a batch on the semiconductor material.
In the semiconductor impurity concentration testing method according to the present invention, a condensed light flux of terahertz pulse light is irradiated onto the semiconductor material, the condensed light flux and the semiconductor material are caused to move relative to each other on the surface of the semiconductor material, transmitted pulse light having been radiated through various points of the semiconductor material is sequentially detected, a spectral transmittance is calculated based upon a time-series waveform of the electric field intensity of the transmitted pulse light and an impurity concentration in the semiconductor material is calculated based upon the spectral transmittance.
Alternatively, in the semiconductor impurity concentration testing method according to the present invention, an expanded light flux achieved by expanding a terahertz pulse light flux is irradiated at once over the entire surface of the semiconductor material, transmitted pulse light having been transmitted through the semiconductor material irradiated with the expanded light flux is detected at once, and a spectral transmittance is calculated based upon a time-series waveform of the electric field intensity of the transmitted pulse light and then an impurity concentration in the semiconductor material is calculated based upon the spectral transmittance.
In either of these semiconductor impurity concentration testing methods, the spectral transmittance is calculated based upon a time-series waveform of the electric field intensity measured by inserting the semiconductor material in the optical path in which the transmitted pulse light is detected and a time-series waveform of the electric field intensity measured without inserting the semiconductor material in the optical path.